Circuit for instant restart of high pressure discharge lamp

ABSTRACT

In the running condition, a high pressure lamp is connected in series with an inductive reactor across the line (240 volts), and a power factor correcting capacitor is connected across the line. To assure instant starting whether the lamp is hot or cold, an igniter is energized which injects kilovolt radio frequency pulses in series with the reactor open circuit voltage across the lamp, and the reactor open circuit voltage is boosted a predetermined factor up to 3 X line voltage by temporarily connecting the power factor correcting capacitor to a tap in the inductive reactor.

Q m United States Patent 1 [11] 3,7524% Wattenbach 1 May 8, 1973 [541 CIRCUIT FOR INSTANT RESTART 0F 3,235,769 2/1966 Wattenbach ..315/DlG.2

HIGH PRESSURE DISCHARGE LAMP 3,508,112 4/1970 Peek 3,644,780 2/1972 Koyama et al. ..3 1 5/100 T [75] Inventor: Hans L. Wattenbach, South Eu- Ohlo Primary Examiner-John Kominski [73] Assignee: General Electric Company, Sche- AttorneyErnest W. Legree et a1.

nectady, NY. 22 Filed: Jan. 28, 1972 [57] ABSTRACT [21] pp No: 221,662 In the running condition, a high pressure lamp is connected in series with an inductive reactor across the I line (240 volts), and a power factor correcting capaci- [52] US C "31 tor is connected across the line. To assure instant 3 3l5/ starting whether the lamp is hot or cold, an igniter is 7 energized which injects kilovolt radio frequency pulses [51] Int. Cl .1105) 41/04 in ries with the reactor open circuit voltage across [58] Field Of Search ..315/l23, I25, 126, the lamp, and the reactor open circuit voltage is 1316- 5, 7 boosted a predetermined factor up to 3 X line voltage by temporarily connecting the power factor correcting [56] Refer n Cited capacitor to a tap in the inductive reactor.

UNITED STATES PATENTS 4 Claims,'2 Drawing Figures 2,373,402 4/1954 Lecorguiller ..3l5/243 5 THETS COUN TEE T/MEE PATENTED HAY 81915 INTEG- STHETS L IGH T COU/VTE E B4702 I B2 L CIRCUIT FOR INSTANT RESTART OF HIGH PRESSURE DISCHARGE LAB/1P BACKGROUND OF THE INVENTION High intensity discharge lamps such as high pressure mercury, sodium or metal halide lamps which develop a relatively high vapor pressure during operation are sometimes difficult to start and usually extremely difficult to restart immediately should they become extinguished after having attained normal operating temperature. The lamps may become extinguished as a result of a severe line voltage dip or during a power failure. If the lamps are allowed to cool down for several minutes in order to allow the metal vapor pressure to drop, they may be restarted. The intervening several minutes of outage have generally been regarded as an inevitable drawback of such lighting installations. However the capability of instant restart is a desirable one in most installations and is essential in some installations such as stadium lighting or operation of printing machines in order to avoid loss of time.

In order to ionize the gases in the arc chamber of a high pressure metal vapor lamp under all temperature conditions whether hot or cold, a high voltage of about to 20 kilovolts peak is required for a lamp having an arc drop of about 100 volts. To transform the 60 Hz open circuit voltage to 10-20 kilovolts in conventional fashion is not only uneconomical but also highly dangerous. High voltages for ignition purposes can be obtained more easily by the use of igniters which superimpose or inject kilovolt radio-frequency pulses in series with the open circuit voltage of the ballast or reactor across the lamp. However I have found that while such igniters will ionize the gases in the lamps and cause a spark discharge, many lamps still fail to start. Particularly, lamps which were previously operating fail to hotrestart and must be allowed to cool down before they will restart.

SUMMARY OF THE INVENTION In accordance with my invention, I have found that in the circumstances recited above wherein the igniter will cause the gases to break down in a spark discharge and the lamp fails to start, the lamp will start if the 60 Hz open circuit voltage is increased. Generally a higher 60 Hz open circuit voltage is required for a hot-restart than for a cold-start, and increase in the open circuit voltage by a factor up to 3 is sufiicient for most cases.

While a higher 60 Hz voltage could be used to resolve the problem, this is not a practical solution because a higher line voltage is not always available and a step up transformer is bulky and costly. If a higher line voltage is available, a reactor and power factor correcting capacitor of larger size and higher cost are needed and the solution is uneconomic.

In accordance with my invention, I utilize the power factor correcting capacitor of an inductive reactor type ballast as a series capacitor at starting to boost the 60 Hz open circuit voltage relative to the line voltage. The open circuit voltage can be increased to as must as 3 times the line voltage by tapping the reactor and connecting the capacitor to the tap by means of a suitable switch or by the use of semiconductors.

In the running condition, the lamp is connected in series with the inductive reactor across the line (240 volts), and the capacitor is connected across the line for power factor compensation. An igniter has its output coil connected in series with the reactor and the lamp across the line but it is not energized. To assure instant start or restart, the igniter is energized whereby it injects kilovolt radio-frequency pulses in series with the reactor open circuit voltage across the lamp which ionize the hot gases. At the same time the reactor open circuit voltage is boosted by temporarily connecting the power factor correcting capacitor to a tap in the reactor and this permits the transition to are discharge to take place.

DESCRIPTION OF DRAWINGS In the drawings:

FIG. I is a schematic diagram of the basic circuit for instant restarting in accordance with the invention;

FIG. 2 is a schematic diagram of a complete circuit with automated switching sequence which is a preferred embodiment of the invention.

DETAILED DESCRIPTION The embodiment of the invention to be described is a power supply for an ultraviolet printing lamp of the kind described and claimed in copending application Ser. No. 25,672 filed Apr. 6, 1970 by Elmer G. Fridrich, entitled Metal Halide Arc Lamp and assigned to the same assignee as this application. The lamp is a compact very high brightness arc lamp using mercury iodide with an excess of iodine as the discharge medium in the pressure range from about 5 to 20 atmospheres. It produces a high ratio of ultraviolet to visible radiation which makes the lamp particularly suitable for photochemical applications requiring a point source for high definition.

The specific lamp used is rated at 2,000 watts and operates with a 1 10 volt drop at 20 amperes. It is used in conjunction with an ultraviolet optical system described and claimed in copending application Ser. No. 253,475 filed May 15, 1972 by Elmer G. Fridrich entitled Wide Angle Optical System for Uniform Printing, and assigned to the same assignee as this invention. The optical system is used to transfer the information from a negative to a photosensitive aluminum printing plate (Diazoplate) in the offset printing process.

The basic power supply in accordance with my invention is shown schematically in FIG. 1 and comprises a current limiting reactor L, a power factor correcting capacitor Cpf, a high voltage, high frequency igniter represented by dotted rectangle 1, and a switching control system which is here represented in greatly simplified form by the single pole double throw switch S. The lamp Lp is connected in series with the output coil of the igniter and the reactor across a 240 volts, Hz line. In the running condition, that is in the operating condition after the lamp has been started, switch S is thrown to position r placing capacitor C across the line where it serves to balance the lagging power factor current drawn by the reactor and lamp and the igniter is not energized. Capability to restart the lamp whether cold or hot is provided by energizing the igniter and throwing switch S to position s whereby the capacitor C is connected to a tap t in the reactor. Practical boost factors extend from about 1.2 to 3. In this embodiment, the line voltage is stepped up by a factor of 1.5 from 240 volts to 360 volts. After the lamp has started, the igniter is de-energized and switch S is returned to position r to restore capacitor C to its power factor correcting role. The circuit may be used to provide a step up by a factor of as much as 3 where desirable, but for open circuit voltage to line voltage ratios greater than 2.0, care must be taken in the design of the reactor to avoid saturation of its core.

LAMP DATA AND BALLAST DESIGN FORMULAS To illustrate the design of a circuit in accordance with the invention, the following typical known data may be assumed from which the required unknown data may be derived as indicated.

Lamp Operating Wattage: W 2,000W

Lamp Operating Voltage: V 100V Lamp Operating Current: I A

Line Voltage: V 240V Line Power Factor: PF 100% Open Circuit Voltage Ratio: m 36OV/24OV 1.5 The reactor impedance X to provide 20 amperes through the lamp under the given conditions is as follows:

XL LN/ Lp) V 1 Lp/ 110 109 Ohms The impedance of the capacitor required to just balance the lagging power factor component of lamp current is as follows:

C l/X 200 microfarad The location of the reactor tap t can be determined as follows, wherein percentage of total number of turns counting from the line side, and

m ratio of open circuit voltage of the ballast with the capacitor at the reactor tap to the open circuit voltage with no capacitor at the reactor tap.

For a value of m 1.5, k is approximately 0.5 and this places the tap about in the middle of the reactor. However in the foregoing equations, the lamp has been assumed to be an ideal resistive load, and some .correction for the nonlinearity of the actual lamp is required. A suitable correction consists in using a lamp having a voltage of 110 volts rather than 100 volts in order to compensate for the lamps power factor of about 90 percent.

While the simple circuit of FIG. 1 can be used to effect the purpose of my invention, it requires knowledge and skill on the part of the operator and is inconvenient. Difficulties may arise where switch S has to interrupt a large inductive load. When switch S disconnects the capacitor from the reactor tap, an arc may form which may last until the capacitor is connected to the line side of the reactor. In such case the arc would short circuit part of the reactor and the lamp and the switch could be severely damaged. An improved system which overcomes these problems and automatically performs the required functions is desirable.

AUTOMATED CIRCUIT OPERATION A preferred circuit according to the invention utilizing relays and switches for automation is illustrated in FIG. 2. All relays are shown in their rest or unergized condition. The operation of the circuit is as follows:

1. To start the lamp, push-button On which is normally open is pressed, closing the circuit. The coil of mains relay A is energized and contacts A1 and A2 close, connecting the unit to the 240 volt power line.

2. After the On push-button is released, relay A is held in by contact LH and the normally closed Off push-button which form a holding loop.

3. The closing of contact A2 also applied voltage to the Timer, the Hours Meter, and relay coil E. Energization of relay coil E caused contact E1 to close and connect the fan to the volt line for cooling the lamp.

4. Immediately after being energized, the Timer causes contact T1 and T2 to close, the latter energizing relay coil B.

5. Contact B1 disconnects the power factor capacitor Cpf from the line and activates relay coil C. Contact B2 initiates the lgniter and the Starts Counter.

6. Contact C1 now closes and connects capacitor Cpf to the reactor tap. This sequence assures that Bl opens before C l closes and allows time for an arc in the gap at B1 to deionize before Cl closes.

7. With capacitor Cpf now connected across the line to the tap in the reactor, the open circuit voltage rises from 240 to 360 volts.

8. The igniter may be conventional and comprises a step up 60 Hz transformer 5, a radio frequency choke coil 6 and a spark gap 7. The spark gap is shunted by a capacitor 8 and the primary 9 of an air or ferrite magnetic core transformer 10 whose secondary 11 is connected in series with the reactor and the lamp across the 240 volt line.

9. When contact B2 closed, the igniter primary was energized and capacitor 8 charged until the breakdown voltage of gap 7 is exceeded. An oscillatory discharge then takes place across the gap and a damped radio frequency oscillation of 20 to 30 kilovolts is coupled through secondary 11 into the lamp circuit. Several such oscillations may be generated per cycle of line voltage. i

10. The combination of the rise in open circuit voltage and the kilovolt pulses from the igniter is sufficient to start the lamp and after a quarter second, the timer turns off opening contacts T1 and T2. Relay coil C is de-energized first because relay coil B remains connected to the line via contact C2.

1 l. Contact Cl disconnects capacitor Cpf from the reactor tap, and the reactor and lamp henceforth operate in the normal running mode.

12. Contact C2 also opens allowing coil B to deenergize whereupon contact B1 connects capacitor Cpf back to the line to perform its normal power factor correcting function. This sequence assures that Cl opens before Bl closes and allows time for an arc in the gap at C l to deionize before Bl closes.

13. Contact B2 turns off the Igniter and starts the Light Integrator which responds to the intensity of ultraviolet radiation and its time duration.

14. When the Light Integrator has measured a preset value corresponding to a desired exposure of the film plate, it causes contact LIl to open so that relay coil A is deenergized.

15. Contacts Al and A2 turn off the lamp, the Hours Meter, the Light Integrator, relay E, and the Timer. Contact A2 connects resistor Rd across the power factor capacitor and discharges it rapidly as a safety precaution.

16. The Light Integrator and the Timer reset themselves for the next use.

17. If the temperature inside the power supply housing rises above a safe value (50 C), the fan will stay on via the contact of a thermal switch 12 until adequate cooling has been achieved.

While the invention has been described in conjunction with an ultraviolet photo-printing application, its utility is not limited thereto and extends generally to high intensity discharge lamp application requiring instantaneous start capability. The switching functions have been described as carried out in a system utilizing switches and relays but with suitable modifications, semiconductors can be utilized to perform equivalent functions.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A circuit for operating a high pressure vapor discharge lamp with instant start capability comprising:

a current-limiting inductive reactor for connection to one side of an alternating current supply line in series with the lamp connected to the other side of the line, said reactor having an intermediate tap therein;

a power factor correcting capacitor;

an igniter for producing kilovolt radio-frequency pulses and including a radio-frequency transformer having an output winding connected in series with said reactor for injecting said pulses superimposed on the reactor open circuit voltage, across the p;

and switching means having a starting position wherein said capacitor is connected from the opposite side of the line to the tap in said reactor and a running position wherein said capacitor is connected across the line, said switching means including means to energize said igniter when in the starting position.

2. A circuit as defined in claim 1 wherein the reactor open circuit voltage is boosted by a factor up to 3 when the power-factor correcting capacitor is connected to said tap.

3. A circuit as defined in claim 1 wherein the reactor impedance is proportioned to limit lamp current substantially to its rated value, the power factor correcting capacitor is proportioned substantially to balance the lagging current drawn by the reactor and lamp in the running position, and the tap in reactor is so located that the reactor open circuit voltage is boosted by a factor up to 3 in the starting condition.

4. A circuit as defined in claim 1 wherein said switching means comprises a mains relay for closing the circuit to the current supply line, said mains relay having a holding loop, switching relays, a timer, and a light integrator, said switching relays being interconnected with said timer whereby they are held in said starting position for a given time interval after the mains relay is energized and then held in said running position, said light integrator being linked with said holding loop to disable said mains relay upon measuring a predetermined time-radiation value. 

1. A circuit for operating a high pressure vapor discharge lamp with instant start capability comprising: a current-limiting inductive reactor for connection to one side of an alternating current supply line in series with the lamp connected to the other side of the line, said reactor having an intermediatE tap therein; a power factor correcting capacitor; an igniter for producing kilovolt radio-frequency pulses and including a radio-frequency transformer having an output winding connected in series with said reactor for injecting said pulses superimposed on the reactor open circuit voltage, across the lamp; and switching means having a starting position wherein said capacitor is connected from the opposite side of the line to the tap in said reactor and a running position wherein said capacitor is connected across the line, said switching means including means to energize said igniter when in the starting position.
 2. A circuit as defined in claim 1 wherein the reactor open circuit voltage is boosted by a factor up to 3 when the power-factor correcting capacitor is connected to said tap.
 3. A circuit as defined in claim 1 wherein the reactor impedance is proportioned to limit lamp current substantially to its rated value, the power factor correcting capacitor is proportioned substantially to balance the lagging current drawn by the reactor and lamp in the running position, and the tap in said reactor is so located that the reactor open circuit voltage is boosted by a factor up to 3 in the starting condition.
 4. A circuit as defined in claim 1 wherein said switching means comprises a mains relay for closing the circuit to the current supply line, said mains relay having a holding loop, switching relays, a timer, and a light integrator, said switching relays being interconnected with said timer whereby they are held in said starting position for a given time interval after the mains relay is energized and then held in said running position, said light integrator being linked with said holding loop to disable said mains relay upon measuring a predetermined time-radiation value. 